Vehicle transmission systems, cooling systems, and braking systems may employ clutches or like devices to selectively transmit rotational forces from a drive source to an output member. For example, some cooling systems employ fan clutches that control the output rotation of engine cooling fans. Such a fan clutch can be driven by a drive pulley that rotates in response to the vehicle engine.
In general, the clutch can be operated to engage (or disengage) opposing clutch surfaces, which rotationally interconnect (or rotationally disconnect) the drive pulley and the output member. In an example related to fan clutches, when the clutch surfaces shifted to the engaged position, the output member (carrying fan blades) is driven to rotate along with the drive pulley. When the fan blades are spinning, an axial thrust can be generated that urges the output member axially away from the drive pulley. A bias spring can be used to maintain the engagement between the input and output members (and the opposing clutch surfaces), but the fan thrust can increase the likelihood of slippage between the input and output members. Also, in some circumstances, the fan thrust can overcome the spring bias and cause the opposing clutch surfaces to temporarily disengage.